f2fs: fix to recover xattr node block

If a new xattr node page was allocated and its inode is fsynced, we should
recover the xattr node page during the roll-forward process after power-cut.
But, previously, f2fs didn't handle that case, resulting in kernel panic as
follows reported by Tom Li.

BUG: unable to handle kernel paging request at ffffc9001c861a98
IP: [<ffffffffa0295236>] check_index_in_prev_nodes+0x86/0x2d0 [f2fs]
Call Trace:
 [<ffffffff815ece9b>] ? printk+0x48/0x4a
 [<ffffffffa029626a>] recover_fsync_data+0xdca/0xf50 [f2fs]
 [<ffffffffa02873ae>] f2fs_fill_super+0x92e/0x970 [f2fs]
 [<ffffffff8112c9f8>] mount_bdev+0x1b8/0x200
 [<ffffffffa0286a80>] ? f2fs_remount+0x130/0x130 [f2fs]
 [<ffffffffa0285e40>] f2fs_mount+0x10/0x20 [f2fs]
 [<ffffffff8112d4de>] mount_fs+0x3e/0x1b0
 [<ffffffff810ef4eb>] ? __alloc_percpu+0xb/0x10
 [<ffffffff8114761f>] vfs_kern_mount+0x6f/0x120
 [<ffffffff811497b9>] do_mount+0x259/0xa90
 [<ffffffff810ead1d>] ? memdup_user+0x3d/0x80
 [<ffffffff810eadb3>] ? strndup_user+0x53/0x70
 [<ffffffff8114a2c9>] SyS_mount+0x89/0xd0
 [<ffffffff815feae2>] system_call_fastpath+0x16/0x1b

This patch adds a recovery function of xattr node pages.
Reported-by: NTom Li <biergaizi@members.fsf.org>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -1121,6 +1121,7 @@ void alloc_nid_done(struct f2fs_sb_info *, nid_t);
 void alloc_nid_failed(struct f2fs_sb_info *, nid_t);
 void recover_node_page(struct f2fs_sb_info *, struct page *,
 		struct f2fs_summary *, struct node_info *, block_t);
+bool recover_xattr_data(struct inode *, struct page *, block_t);
 int recover_inode_page(struct f2fs_sb_info *, struct page *);
 int restore_node_summary(struct f2fs_sb_info *, unsigned int,
 				struct f2fs_summary_block *);

fs/f2fs/node.c

@@ -1535,6 +1535,46 @@ void recover_node_page(struct f2fs_sb_info *sbi, struct page *page,
 	clear_node_page_dirty(page);
 }
 
+bool recover_xattr_data(struct inode *inode, struct page *page, block_t blkaddr)
+{
+	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
+	nid_t prev_xnid = F2FS_I(inode)->i_xattr_nid;
+	nid_t new_xnid = nid_of_node(page);
+	struct node_info ni;
+
+	if (ofs_of_node(page) != XATTR_NODE_OFFSET)
+		return false;
+
+	/* 1: invalidate the previous xattr nid */
+	if (!prev_xnid)
+		goto recover_xnid;
+
+	/* Deallocate node address */
+	get_node_info(sbi, prev_xnid, &ni);
+	f2fs_bug_on(ni.blk_addr == NULL_ADDR);
+	invalidate_blocks(sbi, ni.blk_addr);
+	dec_valid_node_count(sbi, inode);
+	set_node_addr(sbi, &ni, NULL_ADDR);
+
+recover_xnid:
+	/* 2: allocate new xattr nid */
+	if (unlikely(!inc_valid_node_count(sbi, inode)))
+		f2fs_bug_on(1);
+
+	remove_free_nid(NM_I(sbi), new_xnid);
+	get_node_info(sbi, new_xnid, &ni);
+	ni.ino = inode->i_ino;
+	set_node_addr(sbi, &ni, NEW_ADDR);
+	F2FS_I(inode)->i_xattr_nid = new_xnid;
+
+	/* 3: update xattr blkaddr */
+	refresh_sit_entry(sbi, NEW_ADDR, blkaddr);
+	set_node_addr(sbi, &ni, blkaddr);
+
+	update_inode_page(inode);
+	return true;
+}
+
 int recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)
 {
 	struct f2fs_inode *src, *dst;

fs/f2fs/recovery.c

@@ -301,6 +301,9 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
 	if (recover_inline_data(inode, page))
 		goto out;
 
+	if (recover_xattr_data(inode, page, blkaddr))
+		goto out;
+
 	start = start_bidx_of_node(ofs_of_node(page), fi);
 	if (IS_INODE(page))
 		end = start + ADDRS_PER_INODE(fi);